It is known that telephone sets are generally designed to be connected to circuit switched telephone networks, commonly designated by the abbreviation "STN", which convey sound and in particular speech in the form of analog signals, or increasingly in the form of digital signals over at least a portion of the path followed by said signals, each call involving setting up a determined circuit for the duration of the call. Usually, the sound signals to be transmitted from a source in digital form are pre-sampled and pre-encoded using a standardized method, usually in the encoding portion of a codec. The samples obtained are transmitted periodically sample-by-sample, when they are conveyed via a digital telephone network, or when the call is of the circuit type.
Furthermore, terminals exist that are designed to communicate data put in digital form and grouped together in packets. Some such terminals can transmit and/or receive data corresponding to digitized sound signals, and such terminals are sometimes organized to be connected to the same links as telephone sets.
Such terminals are in particular personal computers provided with means enabling them to communicate with remote other data terminals and in particular with other computers, such as those of servers, via a link that parents them on a network making it possible to transmit data asynchronously in packets, said link optionally being a telephone link of the analog type, if the computer is provided with means including a modem.
Asynchronous transmission of digital data in packets can be performed entirely via leased links, and is thus liable to be at least locally performed via links of the switched telephone network, which links are governed synchronously.
The codecs used in telephone sets for digitally processing sound signals, in particular those corresponding to speech signals, and the telephone modems used to convert the digital data signals are often connected to the same telephone links. However, such codecs and modems generally do not enable the apparatuses they respectively serve to communicate with one another insofar as the signalling they respectively use and the communications protocols they implement are in practice at least partially exclusive even though they are technically compatible.
More generally, because of the differences existing between communications protocols using circuits and communications protocols using packets, it is generally not possible to cause apparatuses to communicate when one apparatus uses a circuit communications protocol and the other apparatus uses a packet communications protocol.
Furthermore, it is conventional to associate an answering and/or recording machine with a telephone set to enable users of said telephone set to cause a sound message to be transmitted to callers of the set via the telephone line and to record any sound messages transmitted to the set by such callers.
Such an operation is also possible with apparatuses such as computers which are designed to communicate data in packets between them, since digitized sound signals can also be transmitted in this form, as can be the case in particular for computers connected to the Internet.
As a result, the user of a suitably equipped computer can make use of an answering machine and/or sound message recorder function.
Telephone sets using circuit communications protocols and computers using packet communications protocols do not however make it possible for a user having a telephone and a computer, either or both of which have an answering-recording function, to consult the sound messages left by other users in the computer by means of the telephone and/or vice versa.
This can be particularly inconvenient for a person away on a trip who has access to a communications network via an apparatus that enables said person to call the apparatus in which the messages recorded for him or her are located but does not enable genuine communications to take place because of the incompatibilities that exist between the communications protocols implemented by the apparatuses used.